Merge remote-tracking branch 'nsz/math'

[musl] / src / math / fma.c

diff --git a/src/math/fma.c b/src/math/fma.c
index 5fb9540..17f1cdc 100644 (file)
--- a/src/math/fma.c
+++ b/src/math/fma.c
@@ -41,7 +41,7 @@ static void mul(long double *hi, long double *lo, long double x, long double y)
 
 /*
 assume (long double)(hi+lo) == hi
-return an adjusted hi so that rounding it to double is correct
+return an adjusted hi so that rounding it to double (or less) precision is correct
 */
 static long double adjust(long double hi, long double lo)
 {
@@ -55,17 +55,25 @@ static long double adjust(long double hi, long double lo)
        ulo.x = lo;
        if (uhi.bits.s == ulo.bits.s)
                uhi.bits.m++;
-       else
+       else {
                uhi.bits.m--;
+               /* handle underflow and take care of ld80 implicit msb */
+               if (uhi.bits.m == (uint64_t)-1/2) {
+                       uhi.bits.m *= 2;
+                       uhi.bits.e--;
+               }
+       }
        return uhi.x;
 }
 
+/* adjusted add so the result is correct when rounded to double (or less) precision */
 static long double dadd(long double x, long double y)
 {
        add(&x, &y, x, y);
        return adjust(x, y);
 }
 
+/* adjusted mul so the result is correct when rounded to double (or less) precision */
 static long double dmul(long double x, long double y)
 {
        mul(&x, &y, x, y);
@@ -81,6 +89,7 @@ static int getexp(long double x)
 
 double fma(double x, double y, double z)
 {
+       #pragma STDC FENV_ACCESS ON
        long double hi, lo1, lo2, xy;
        int round, ez, exy;
 
@@ -298,6 +307,7 @@ static inline struct dd dd_mul(double a, double b)
  */
 double fma(double x, double y, double z)
 {
+       #pragma STDC FENV_ACCESS ON
        double xs, ys, zs, adj;
        struct dd xy, r;
        int oround;